If I'm decades from retirement, is it a mistake to own any bonds at all?

Not necessarily, but there's a real debate here. Financially, a young investor with a stable income and long horizon can justify an all-stock portfolio, since decades of runway let them ride out even severe crashes, and stocks have historically outgrown bonds over long periods. Some experts argue holding bonds early on unnecessarily drags returns.

The counterargument is behavioral and practical. A small bond allocation (say 10%) gives you something stable to rebalance from when stocks crash, and it can prevent panic-selling during your first big downturn, which is worth far more than a few tenths of a percent in expected return. If you know you'll stay the course no matter what, near-100% stocks is defensible. If a 40% drop early in your career might scare you out of the market, a modest bond sleeve is cheap insurance for your own behavior.